Methods for actively controlling RF peak-to-peak voltage in an inductively coupled plasma etching system

ABSTRACT

An inductively coupled plasma etching apparatus includes a chamber and a window for sealing a top opening of the chamber. The window has an inner surface that is exposed to an internal region of the chamber. A metal plate, which acts as a Faraday shield, is disposed above and spaced apart from the window. A coil is disposed above and spaced apart from the metal plate. The coil is conductively connected to the metal plate at a connection location that is configured to generate a peak-to-peak voltage on the metal plate that optimally reduces sputtering of the inner surface of the window while substantially simultaneously preventing deposition of etch byproducts on the inner surface of the window. In another embodiment, the apparatus includes a controller for externally applying a peak-to-peak voltage to the metal plate. The controller includes an oscillation circuit, a matching circuit, an RF generator, and a feedback control for monitoring the applied peak-to-peak voltage. Methods for optimizing operation of an inductively coupled plasma etching apparatus also are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. application Ser. No.09/676,462, filed Sep. 29, 2000, which is a continuation-in-part ofapplication Ser. No. 09/608,883, filed Jun. 30, 2000. The disclosures ofthese applications, from which priority under 35 U.S.C. §120 is claimed,are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to semiconductorfabrication and, more particularly, to methods for controlling theplasma behavior inside of plasma etching chambers.

[0003] In semiconductor manufacturing processes, etching processes,insulation film formation, and diffusion processes are repeatedlycarried out. As is well known to those skilled in the art, there are twotypes of etching processes: wet etching and dry etching. Dry etching istypically implemented by using an inductively coupled plasma etchingapparatus such as shown in FIG. 1A.

[0004] In the inductively coupled plasma etching apparatus shown in FIG.1A, a reactant gas is first led into chamber 20 through a gas lead-inport (not shown). High frequency power is then applied from a powersupply (not shown) to coil 17. Semiconductor wafer 11 is mounted onchuck 19 provided inside chamber 20. Coil 17 is held on the upperportion of the chamber by spacers 13, which are formed of an insulatingmaterial. In operation, high frequency (RF) current passing through coil17 induces an electromagnetic current into chamber 20, and theelectromagnetic current acts on the reactant gas to generate a plasma.

[0005] The plasma contains various types of radicals and the chemicalreaction of the positive/negative ions is used to etch semiconductorwafer 11 itself or an insulation film formed on the wafer. During theetching process, coil 17 carries out a function that corresponds to thatof the primary coil of a transformer while the plasma in chamber 20carries out a function that corresponds to that of the secondary coil ofthe transformer. The reaction product generated by the etching processis discarded via exhaust port 15.

[0006] When etching one of the recently developed device materials(e.g., platinum, ruthenium, and the like), the reaction productgenerated may be a nonvolatile substance (e.g., RuO₂). In some cases,the reaction product may adhere to surface 10 a of TCP window 10. If thereaction product is conductive, then the film of reaction product onsurface 10 a may electrically shield the electromagnetic current in thechamber. Consequently, the plasma does not strike well after severalwafers are etched and the etching process must be discontinued.

[0007] In an effort to avoid this problem, a method for sputtering thereaction product adhered to surface 10 a of TCP window 10 by using theplasma has been developed. In the inductively coupled plasma etchingapparatus shown in FIG. 1A, however, the electromagnetic current inducedby the RF current generates a distribution voltage having a standingwave in the vicinity of TCP window 10. This is problematic because itcauses the deposition and sputtering of the reaction product to becomenonuniform.

[0008]FIGS. 1B and 1C illustrate the inherent nonuniformity of thedeposition and sputtering on the TCP window in the inductively coupledplasma etching apparatus shown in FIG. 1A. In FIG. 1B, coil 17 isindicated by boxes having either an “x” or a “” therein. The boxeshaving an “x” therein indicate that the coil extends into the page. Theboxes having a “” therein indicate that the coil extends out of thepage. As shown in FIG. 1B, some portions of surface 10 a of TCP window10 are subjected to excess sputtering and other portions of the surfaceare subjected to excess deposition. Excess sputtering occurs in theregions where a relatively large amount of energy is added to the ionsin the plasma because the amplitude of the acceleration voltage due tothe standing wave at the location is high. As shown in the graph in thelower part of FIG. 1C, the amplitude of standing wave 24 is high atpoints 24 a and 24 b, which correspond to ends 17 a and 17 b,respectively, of coil 17, as shown in the upper part of FIG. 1C. Excessdeposition occurs in the regions where only a relatively small amount ofenergy is added to the ions in the plasma because the amplitude of thestanding wave is low. As shown in the graph in the lower part of FIG.1C, the amplitude of standing wave 24 is low in the region proximate topoint 22, which is the node of the standing wave.

[0009] Nonuniform deposition and sputtering on the TCP window isundesirable for a number of reasons. Excessive deposition is undesirablebecause, as discussed above, the presence of an electrically conductivefilm on the surface of the TCP window can electrically shield theelectromagnetic current in the chamber and thereby disable the etchingprocess. In addition, excessive deposition often causes particleproblems (particles flake off on the wafer) and, consequently, increasesthe frequency with which the chamber must be subjected to dry and wetcleanings. Frequent cleaning of the chamber is particularly undesirablebecause it sacrifices the tool's available up time and thereby reducesthroughput. Excessive sputtering is undesirable because the ionbombardment can cause erosion of the TCP window, which is typically madeof quartz or alumina. Such erosion not only shortens the lifetime of theTCP window, but also generates particles, which can contaminate thewafer and introduce unwanted chemical species into the processenvironment. The presence of unwanted chemical species in the processenvironment is particularly undesirable because it leads to poorreproducibility of the process conditions.

[0010] In view of the foregoing, there is a need for an inductivelycoupled plasma etching apparatus that prevents substantial deposition ofelectrically conductive reaction products on the surface of the TCPwindow without causing excess erosion of the TCP window.

SUMMARY OF THE INVENTION

[0011] Broadly speaking, the present invention provides an inductivelycoupled plasma etching apparatus that uniformly adds energy to the ionsin the plasma in the vicinity of a wall of the chamber in which theplasma is generated.

[0012] In one aspect of the invention, a first type of inductivelycoupled plasma etching apparatus is provided. This inductively coupledplasma etching apparatus includes a chamber and a window for sealing atop opening of the chamber. The window has an inner surface that isexposed to an internal region of the chamber. A metal plate, which actsas a Faraday shield, is disposed above and spaced apart from the window.A coil is disposed above and spaced apart from the metal plate. The coilis conductively connected to the metal plate at a connection locationthat is configured to generate a peak-to-peak voltage on the metal platethat optimally reduces sputtering of the inner surface of the windowwhile substantially simultaneously preventing deposition of etchbyproducts on the inner surface of the window.

[0013] In one embodiment, the inductively coupled plasma etchingapparatus further includes a coil input terminal for receiving RF powerand a coil output terminal. In this embodiment, the connection locationis defined between the coil input terminal and the coil output terminal.In one embodiment, the connection location is more proximate to the coiloutput terminal than to the coil input terminal. In one embodiment, theinductively coupled plasma etching apparatus further includes an RFgenerator, a match circuit network coupled between the RF generator andthe coil input terminal, and a variable capacitor coupled between groundand the coil output terminal.

[0014] In one embodiment, the inductively coupled plasma etchingapparatus further includes an oscillation circuit coupled to the metalplate. The oscillation circuit is controllable so that the peak-to-peakvoltage on the metal plate may be adjusted. In one embodiment, theoscillation circuit includes a variable capacitor that can be adjustedto control the peak-to-peak voltage along a harmonic point. In anotherembodiment, the inductively coupled plasma etching apparatus furtherincludes a voltage divider circuit coupled to the metal plate. Thevoltage divider circuit is controllable so that the peak-to-peak voltagemay be adjusted. In one embodiment, the voltage divider circuit includesa variable capacitor that can be adjusted to control the peak-to-peakvoltage along a plot that decreases the peak-to-peak voltage ascapacitance of the variable capacitor increases.

[0015] In one embodiment, the inductively coupled plasma etchingapparatus includes a chamber lid that is configured to have attachedthereto the metal plate and the coil. The chamber lid may be attached byhinges that enable opening and closing of the chamber lid. When in aclosed position, the chamber lid places the metal plate proximate to thewindow in preparation for operation.

[0016] In another aspect of the invention, a second type of inductivelycoupled plasma etching apparatus is provided. This inductively coupledplasma etching apparatus includes a chamber and a window for sealing atop opening of the chamber. The window has an inner surface that isexposed to an internal region of the chamber. A metal plate, which actsas a Faraday shield, is disposed above and spaced apart from the window.A coil is disposed above and spaced apart from the metal plate. Theapparatus also includes a controller for externally applying apeak-to-peak voltage to the metal plate. The controller includes anoscillation circuit, a matching circuit, an RF generator, and a feedbackcontrol for monitoring the applied peak-to-peak voltage.

[0017] In one embodiment, the externally applied peak-to-peak voltage isadjustable so as to reduce sputtering of the inner surface of the windowwhile substantially simultaneously preventing deposition of etchbyproducts on the inner surface of the window. In one embodiment, theinductively coupled plasma etching apparatus further includes a coilinput terminal for receiving RF power and a coil output terminal. In oneembodiment, the inductively coupled plasma etching apparatus furtherincludes an RF generator, a match circuit network coupled between the RFgenerator and the coil input terminal, and a variable capacitor coupledbetween ground and the coil output terminal.

[0018] In one embodiment, the metal plate is connected to the window bydielectric spacers. In one embodiment, the inductively coupled plasmaetching apparatus includes a chamber lid that is configured to haveattached thereto the metal plate and the coil. The chamber lid may beattached by hinges that enable opening and closing of the chamber lid.When in a closed position, the chamber lid places the metal plateproximate to the window in preparation for operation. When in an openposition, the chamber lid places the metal plate away from the windowfor visual inspection of the window and servicing of the chamber.

[0019] In accordance with yet another aspect of the invention, a firstmethod for optimizing operation of an inductively coupled plasma etchingapparatus is provided. In this method, a chamber for etching a wafer issupplied. A window is attached to a top opening of the chamber. Thewindow has an outer surface and an inner surface that is exposed to aninner region of the chamber. A coil is placed over the window and ametal plate is placed over the outer surface of the window. The metalplate is positioned in a spaced apart relationship between the coil andthe outer surface of the window. The metal plate is conductivelyconnected to a connection location on the coil. The connection locationis between an input terminal and an output terminal and is optimallyselected so as to produce substantially uniform incident ion energyproximate to the inner surface of the window. The substantially uniformincident ion energy is configured to reduce sputtering of the innersurface of the window while substantially simultaneously preventingdeposition of etch byproducts on the inner surface of the window.

[0020] In accordance with a still further aspect of the invention, asecond method for optimizing operation of an inductively coupled plasmaetching apparatus is provided. In this method, a chamber for etching awafer is supplied. A window is attached to a top opening of the chamber.The window has an outer surface and an inner surface that is exposed toan inner region of the chamber. A coil is placed over the window and ametal plate is placed over the outer surface of the window. The metalplate is positioned in a spaced apart relationship between the coil andthe outer surface of the window. A controlled peak-to-peak voltage isapplied to the metal plate so as to produce substantially uniformincident ion energy proximate to the inner surface of the window. Thesubstantially uniform incident ion energy is configured to reducesputtering of the inner surface of the window while substantiallysimultaneously preventing deposition of etch byproducts on the innersurface of the window.

[0021] The apparatus and methods of the present invention providenumerous advantages. Most notably, the apparatus and methods of thepresent invention uniformly prevent the deposition of electricallyconductive reaction products, e.g., RuO₂, on the inner surface of theupper wall (e.g., TCP window) of a chamber in an inductively coupledplasma etching system. This increases throughput in the plasma etchingof recently developed device materials, e.g., Ru, because the plasmaetching operation does not have to be stopped to clean the walls of thechamber after only a few wafers have been processed. In addition, theapparatus and methods of the present invention also uniformly preventsputtering of the inner surface of the upper wall (e.g., TCP window) ofa chamber in an inductively coupled plasma etching system. Thisincreases the reproducibility of the process conditions by avoiding thegeneration of particles and the introduction of unwanted chemicalspecies into the process environment.

[0022] It is to be understood that the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated in andconstitute part of this specification, illustrate exemplary embodimentsof the invention and together with the description serve to explain theprinciples of the invention.

[0024]FIG. 1A is a simplified schematic cross-section showing a priorart inductively coupled plasma etching apparatus.

[0025]FIG. 1B is a simplified schematic diagram that illustrates theinherent nonuniformity of the deposition and sputtering on the TCPwindow in the inductively coupled plasma etching apparatus shown in FIG.1A.

[0026]FIG. 1C is a graph that shows the V_(pp) on the coil in theinductively coupled plasma etching apparatus shown in FIG. 1A as afunction of coil length.

[0027]FIG. 2A is a simplified schematic cross-section showing aninductively coupled plasma etching apparatus in accordance with oneembodiment of the present invention.

[0028]FIG. 2B is a simplified schematic cross-section that illustratesthe plasma generation in an inductively coupled plasma etching apparatusin accordance with one embodiment of the invention.

[0029]FIG. 2C is a simplified schematic cross-section that illustratesthe uniform window sputtering obtained by an inductively coupled plasmaetching apparatus in accordance with one embodiment of the invention.

[0030]FIG. 3 is an exploded perspective view of a metal plate, whichacts as a Faraday shield, and the components for holding the metal platein place in accordance with one embodiment of the present invention.

[0031]FIG. 4 is an exploded perspective view of a coil and thecomponents for holding the coil in place in accordance with oneembodiment of the present invention.

[0032]FIG. 5 is a simplified schematic diagram that shows the apparatusand the connection locations used in tests conducted to determine theoptimal location at which to connect the Faraday shield plate to thecoil for ruthenium (Ru) etching.

[0033]FIGS. 6A, 6B, and 6C are graphs showing the measured V_(pp) as afunction of TCP power for the Faraday shield plate, the coil terminalinput, and the coil terminal output, respectively, for each ofconnection locations A, B, and C shown in FIG. 5.

[0034]FIG. 7A is a simplified schematic diagram of an inductivelycoupled plasma etching apparatus including an oscillation circuit toexternally control the V_(pp) of the Faraday shield plate in accordancewith one embodiment of the present invention.

[0035]FIG. 7B is a graph that shows V_(pp) as a function of variablecapacitor position for the inductively coupled plasma etching apparatusshown in FIG. 7A.

[0036]FIG. 8A is a simplified schematic diagram of an inductivelycoupled plasma etching apparatus including a voltage divider circuit toexternally control the V_(pp) of the Faraday shield plate in accordancewith another embodiment of the present invention.

[0037]FIG. 8B is a graph that shows V_(pp) as a function of variablecapacitor position for the inductively coupled plasma etching apparatusshown in FIG. 8A.

[0038]FIG. 9A is a simplified schematic diagram of an inductivelycoupled plasma etching apparatus in which the Faraday shield plate isdriven by a different frequency in accordance with yet anotherembodiment of the present invention.

[0039]FIG. 9B is a graph that shows V_(pp) as a function of lowfrequency RF power for the inductively coupled plasma etching apparatusshown in FIG. 9A.

[0040]FIG. 10 is a graph that shows the ruthenium etch rate as afunction of the number of wafers processed in a conventional inductivelycoupled plasma etching apparatus and an inductively coupled plasmaetching apparatus having a Faraday shield plate that is coupled to thecoil in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Several exemplary embodiments of the invention will now bedescribed in detail with reference to the accompanying drawings. FIGS.1A-1C are discussed above in the “Background of the Invention” section.

[0042]FIG. 2A is a simplified schematic cross-section showing aninductively coupled plasma etching apparatus in accordance with oneembodiment of the present invention. As shown in FIG. 2A, semiconductorwafer 11 is mounted on chuck 19 disposed in chamber 100, which isdefined by walls of a housing, proximate to a lower wall of the housing.Coil 117 is supported on TCP window 10 of chamber 100 by spacers 13,which may be formed of an insulating material. TCP window 10 ispreferably made of quartz; however, other materials such as alumina(Al₂O₃), silicon nitride (Si₃N₄), aluminum nitride (AlN), siliconcarbide (SiC), and silicon (Si) also may be used. The primary role ofTCP window 10 is to provide a vacuum seal to chamber 100. In oneembodiment, TCP window 10 is separated from wafer 11 by a distance thatis between about 2 inches and about 8 inches, and more preferablybetween about 4 inches and about 5 inches. In operation, a reactant gasis fed into chamber 100 through a gas lead-in port (not shown). Highfrequency power from a power supply (not shown) is applied to coil 117.The high frequency (RF) current passing through coil 117 induces anelectromagnetic current in chamber 100, and the electromagnetic currentacts on the reactant gas to generate a plasma.

[0043] The plasma contains various types of radicals and the chemicalreaction of the positive/negative ions is used to etch semiconductorwafer 11 itself or an insulation film formed on the wafer. During theetching process, coil 117 carries out a function that corresponds tothat of the primary coil of a transformer while the plasma in chamber100 carries out a function that corresponds to that of the secondarycoil of the transformer. If the reaction product generated by theetching process is volatile, then this reaction product is discarded viaexhaust port 15.

[0044] Metal plate 217, which acts as a Faraday shield, is providedbetween coil 117 and chamber 100. For ease of reference, metal plate 217is also referred to herein as “the Faraday shield plate.” In oneembodiment, metal plate 217 is positioned in a spaced apart relationshipbetween coil 117 and TCP window 10 and is substantially parallel to theTCP window. The thickness of metal plate 217 is preferably between about20 μm and about 10 mm, and more preferably between about 50 μm and about5 mm. In one embodiment, metal plate 217 has a thickness of about 1.5mm. Connector 207 electrically connects metal plate 217 to coil 117 at apredetermined position of the coil and functions to ensure that thein-plane RF voltage applied to metal plate 217 is uniform. Because thein-plane RF voltage applied to metal plate 217 is uniform, energy isuniformly added to the plasma in the vicinity of TCP window 10. As aresult of this uniform energy distribution, the deposition andsputtering of the reaction product occurs uniformly so that undesirableaccumulation of the reaction product on TCP window 10 does not occur oris substantially eliminated.

[0045] In one embodiment, connector 207 electrically connects metalplate 217 to coil 117 at a position so that adequate V_(pp)(peak-to-peak voltage) is applied on the metal plate. By uniformlyapplying V_(pp) on metal plate 217, ions in the plasma are acceleratedand uniformly bombard the vacuum side surface of a wall of the chamberof the inductively coupled plasma etching apparatus to preventdeposition of the reaction product thereon. In one embodiment, theinductively coupled plasma etching apparatus is a TCP 9400 PTX plasmaetching apparatus, which is commercially available from Lam ResearchCorporation of Fremont, Calif., and the accelerated ions uniformlybombard the vacuum side surface of the TCP window to prevent depositionof the reaction product thereon. In an alternative embodiment, connector207 electrically connects metal plate to a conductor extending from animpedance matching box to the coil.

[0046]FIGS. 2B and 2C illustrate the uniform window sputtering obtainedby an inductively coupled plasma etching apparatus in accordance withone embodiment of the invention. As shown in FIG. 2B, the application ofan appropriate V_(pp) to metal plate 217 through connector 207, whichmay be connected to coil 117 at the optimum location for a particularprocess, generates magnetic fields within chamber 100 that are uniformacross the surface of metal plate 217. These uniform magnetic fields inturn induce a uniform electromagnetic current in chamber 100, and thisinductive current acts on the reactant gas to generate a plasma. Becausethe inductive current is uniform across the surface of metal plate 217,the energy of the incident ions that bombard surface 10 a of TCP window10 also is uniform, as shown in FIG. 2C.

[0047]FIG. 3 is an exploded perspective view of the metal plate, whichacts as a Faraday shield, and the components for holding the metal platein place in accordance with one embodiment of the invention. As shown inFIG. 3, metal plate 217 is secured to the underside of attachment frame201, which is provided with attachment spacers 13 on a top side thereof,by screws 205. Attachment frame 201, attachment spacers 13, and screws205 may be formed of any suitable insulating material.

[0048] Outer ring 211, inner ring 213, and center disk 215 are securedto attachment frame 201 by screws 219, which may be formed of anysuitable insulating material. Outer ring 211, inner ring 213, and centerdisk 215 retain the shape of metal plate 217 during operation of theinductively coupled plasma etching apparatus. A plurality of radialslots 221 is formed in metal plate 217. Radial slots 221 extendtransversely to the sections of coil 117 (see FIG. 4) to interrupt aninternal induced power generated by electric current from flowing onmetal plate 217, which is a conductor. This is necessary becauseelectric current flowing on metal plate 217 causes coil 117 (see, e.g.,FIGS. 2A and 4) and chamber 100 (see, e.g., FIG. 2A) to be electricallyshielded.

[0049] With continuing reference to FIG. 3, connector 207 electricallyconnects metal plate 217 and coil 117 (see, e.g., FIGS. 2A and 4). Twometal screws 209 are used to make this connection, with one metal screwconnecting metal plate 217 to connector 207 and the other metal screwconnecting coil 117 to connector 207.

[0050]FIG. 4 is an exploded perspective view of the coil and thecomponents for holding the coil in place in accordance with oneembodiment of the invention. As shown in FIG. 4, attachment frame 201and attachment spacers 13 are provided between metal plate 217 and coil117. The four ends of cross-shaped coil mounting plate 305 are fixed bysupport spring housings 301 and metal screws 303 to retain the shape ofcoil 117. As shown in FIG. 4, coil 117 has three turns. Coil 117 musthave at least one turn, but otherwise may have any suitable number ofturns as may be needed for the application.

[0051] As discussed above in connection with the description of FIG. 3,connector 207 electrically connects metal plate 217 to coil 117. Asshown in FIG. 4, a U-shaped spacer 309 positions coil mounting plate305, coil 117, and metal plate 217. U-shaped spacer 309 is connected tocoil 117 by metal screw 307. One metal screw 209 electrically connectsconnector 207 to coil 117 through U-shaped spacer 309 and another metalscrew 209 electrically connects connector 207 to metal plate 217 (seeFIG. 3). As shown in FIG. 4, coil 117 is configured so that both thecoil input terminal 117 a and the coil output terminal 117 b aresituated proximate to the center of the coil 117. In particular, coil117 includes coil end 117 a-1 and coil output terminal 117 b. Coilextension 117 a-2 connects coil end 117 a-1 to coil extension end 117a-3 of coil extension 117 a-4. Coil input terminal 117 a is at the otherend of coil extension 117 a-4. It will be apparent to those skilled inthe art that the configuration of the coil may be varied from that shownin FIG. 4 in situations where it is not necessary to have both the coilinput terminal and coil output terminal situated proximate to the centerof the coil 117.

[0052]FIG. 5 is a simplified schematic diagram that shows the apparatusand the connection locations used in tests conducted to determine theoptimal location at which to connect the Faraday shield plate to thecoil for ruthenium (Ru) etching. As shown in FIG. 5, RF generator 400,match circuit network 402, and VI probe 412 a are coupled to coil inputterminal 117 a of coil 117. Variable capacitor 401, which is grounded,and VI probe 412 b are coupled to coil output terminal 117 b of coil117. During testing, metal plate 217, i.e., the Faraday shield plate,was coupled to coil 117 by connector 207 at locations A, B, and C andV_(pp) was measured for each of these connection locations at coil inputterminal 117 a and coil output terminal 117 b with VI probes 412 a and412 b, respectively. In addition, V_(pp) of metal plate 217 was measuredfor each of connection locations A, B, and C with VI probe 412 c. VIprobes 412 a, 412 b, and 412 c are capacitive probes including a metalprobe and a metal, e.g., copper, plate separated by a dielectricmaterial, e.g., polyimide.

[0053]FIGS. 6A, 6B, and 6C are graphs showing the measured V_(pp) as afunction of TCP power for metal plate 217, coil input terminal 117 a,and coil output terminal 117 b, respectively, for each of connectionlocations A, B, and C shown in FIG. 5. As shown in FIG. 6A, forconnection location A (near the output), V_(pp) of metal plate 217decreases significantly as the TCP power increases. For connectionlocations B and C, V_(pp) of metal plate 217 increases slightly as theTCP power increases. As shown in FIG. 6B, for each of connectionlocations A, B, and C, V_(pp) at coil input terminal 117 a increasessignificantly as the TCP power increases. As shown in FIG. 6C, forconnection location A, V_(pp) at coil output terminal 117 b decreasesslightly as the TCP power increases. For connection locations B and C,V_(pp) at coil output terminal 117 b increases significantly as the TCPpower increases.

[0054] Referring back to FIG. 6A, connection location A yielded a V_(pp)of 676 volts at 800 watts for metal plate 217. During testing, the TCPwindow remained clean, but there was too much sputtering. Micromaskingof ruthenium was observed with a blasted quartz window, but was resolvedby replacing the blasted quartz window with a polished window.Connection location B yielded a V_(pp) of 464 volts at 800 watts. Duringtesting, no etch byproduct deposition was observed on the TCP windowafter the equivalent of approximately one lot of wafers was subjected toruthenium etching. Connection location C yielded a V_(pp) of 373 voltsat 800 watts. During testing, a light deposition was observed on the TCPwindow after several wafers were etched. Thus, for a ruthenium etchprocess, the foregoing test results demonstrate that connection locationB is superior to connection locations A and C.

[0055] The Faraday shield plate of the present invention is well suitedfor single step etch recipes where the RF peak-to-peak voltage and theRF matching can be optimized for the specific etching recipe. Manyetching recipes, however, include multiple etching steps, e.g., thebreakthrough step, the bulk etch steps, and the over etch step, in whichthe RF power, pressure, and gas compositions can be substantiallydifferent. Consequently, a certain setting of V_(pp) on the Faradayshield plate (e.g., connection location) for a given etch step may notbe optimal in other etch steps. Further, because the etching chamberimpedance varies for different etch steps, RF tuning to satisfy thevarious impedances can be difficult. For an etch recipe that includesmultiple etch steps, each individual etch process can be optimized byselecting just the right connection point to substantially eliminatedeposition of materials on the quartz window. By way of example, suchoptimization can be reached in a manner similar to that which yieldedthe selection of connection location B, as described above withreference to FIG. 5. In that example, the points A, B, and C wereselected to be about 25 mm from the coil output terminal, about 80 mmfrom the coil output terminal, and about 140 mm from the coil outputterminal, respectively. Of course, it will be apparent to those skilledin the art that these locations can and will change depending on therecipe used to etch a given material and the combination of matchingnetwork element settings.

[0056]FIG. 7A is a simplified schematic diagram of an inductivelycoupled plasma etching apparatus including an oscillation circuit toexternally control the V_(pp) of the Faraday shield plate in accordancewith one embodiment of the present invention. As shown in FIG. 7A, RFgenerator 400 and match circuit network 402 are coupled to coil inputterminal 117 a of coil 117. Variable capacitor 401, which is grounded,is coupled to coil output terminal 117 b of coil 117. Metal plate 217 isconnected to coil 117 and to shield box 406, which defines anoscillation circuit including variable capacitor 408 and inductor 409.Variable capacitor 408 and inductor 409 are grounded. With thisconfiguration, the V_(pp) of metal plate 217 can be controlled byadjusting the position of the variable capacitor of the oscillationcircuit. As shown in FIG. 7B, the maximum V_(pp) occurs at the harmonicpoint.

[0057]FIG. 8A is a simplified schematic diagram of an inductivelycoupled plasma etching apparatus including a voltage divider circuit toexternally control the V_(pp) of the Faraday shield plate in accordancewith another embodiment of the present invention. As shown in FIG. 8A,RF generator 400 and match circuit network 402 are coupled to coil inputterminal 117 a of coil 117. Variable capacitor 401, which is grounded,is coupled to coil output terminal 117 b of coil 117. Metal plate 217 isconnected to coil 117 via voltage divider circuit 416, which includescoupling capacitor 416a and variable capacitor 416 b. Metal plate 217 isconnected to voltage divider circuit 416 such that coupling capacitor416 a is disposed between coil 117 and the metal plate and variablecapacitor 416 b is disposed between the metal plate and ground. Withthis configuration, the V_(pp) of metal plate 217 can be controlled byadjusting the position of the variable capacitor of the voltage dividercircuit. As shown in FIG. 8B, V_(pp) is proportional to the divide ratioof the voltage divider circuit.

[0058] On one hand, the configurations for externally controlling theV_(pp) of the Faraday shield plate shown in FIGS. 7A and 8A aredesirable because they are simple and inexpensive. On the other hand,these configurations may affect TCP matching. In this regard, theconfiguration shown in FIG. 7A affects TCP matching to a lesser extentthan does the configuration shown in FIG. 8A.

[0059]FIG. 9A is a simplified schematic diagram of an inductivelycoupled plasma etching apparatus in which the Faraday shield plate isindependently driven by a different frequency in accordance with yetanother embodiment of the present invention. As shown in FIG. 9A, RFgenerator 400 and match circuit network 402 are coupled to coil inputterminal 117 a of coil 117. Variable capacitor 401, which is grounded,is coupled to coil output terminal 117 b of coil 117. Metal plate 217 iscoupled to Faraday shield driver 450 at connection point 462. Faradayshield driver 450 is essentially a controller that enables monitoring ofapplied peak-to-peak voltages at different TCP power settings andon-the-fly adjustments to achieve the most optimal performance withoutdependence on the matching circuitry of coil 117. This is true becauseno connection is made between the coil and the metal plate in thisexemplary embodiment. As shown in FIG. 9A, Faraday shield driver 450includes matching circuit 452, a 13.56 MHz oscillation circuit thatincludes inductor 454 and variable capacitor 456, RF generator 458, andV_(pp) feedback loop 460.

[0060] In operation, RF power from RF generator 458, which is grounded,is applied to metal plate 217. The RF power is preferably in a rangefrom about 50 KHz to about 50 MHz, and more preferably in a range fromabout 100 KHz to just below 13.56 MHz. In one embodiment, the RF poweris about 2 MHz. The 13.56 MHz oscillation circuit, which is coupled tometal plate 217, acts to “ground” the metal plate from a 13.56 MHz pointof view. Stated differently, the 13.56 MHz oscillation circuit shuts outthe interruption from the RF power applied to metal plate 217 by RFgenerator 400.

[0061] The V_(pp) feedback 460 is preferably provided back to RFgenerator 458 for comparison with an external V_(pp) value. Based onthis comparison, adjustments can be made to RF generator 458 so that themost optimal V_(pp) level can be applied to the Faraday shield plate. Ina preferred embodiment, the monitoring of the applied V_(pp) can becontrolled by way of a computer control station. The computer controlstation can provide a user with statistical operational data by way of atext display, a graphical user interface (GUI), or printouts. Based onthis statistical data, the operator can make further adjustments so asto achieve the most optimal performance and thus eliminate thedeposition of byproducts on the inner chamber walls such as, forexample, the TCP window inner surface. Accordingly, with theconfiguration of FIG. 9A, the V_(pp) of metal plate 217 can becontrolled by adjusting the low frequency RF power applied to the metalplate. As shown in FIG. 9B, V_(pp) increases as the low frequency RFpower increases. Therefore, in this exemplary embodiment, there is noneed to have a fixed connection point to coil 117.

[0062]FIG. 10 is a graph that shows the ruthenium etch rate as afunction of the number of wafers processed in a conventional inductivelycoupled plasma etching apparatus and an inductively coupled plasmaetching apparatus having a Faraday shield plate that is coupled to thecoil in accordance with the present invention. As shown in FIG. 10, in aconventional inductively coupled plasma etching apparatus, the rutheniumetch rate decreases by about 50% after 150 wafers have been processed.In contrast, in an inductively coupled plasma etching apparatus having aFaraday shield coupled to the coil in accordance with the presentinvention, the ruthenium etch rate after 150 wafers have been processedis substantially the same as the initial etch rate. Thus, the Faradayshield plate of the present invention provides a highly reproducibleruthenium etch rate.

[0063] The present invention also provides a method for controlling aninner surface of a wall defining a chamber in which a plasma isgenerated in an inductively coupled plasma etching apparatus. In thismethod, a metal plate is provided between a coil for receiving highfrequency (RF) power and the plasma generated in the chamber such thatthe metal plate does not contact the coil. The metal plate has aplurality of metal slits formed therein that extend transversely to thecoil and is electrically connected to the coil, as described above. Aplasma etching operation is conducted in the inductively coupled plasmaetching apparatus. During the plasma etching operation, the depositionof a reaction product on an inner surface of a wall positioned betweenthe metal plate and the plasma and the sputtering of the reactionproduct from the inner surface of the wall are substantially uniform sothat an amount of the reaction product sufficient to disable the plasmaetching operation does not accumulate on the inner surface of the wall.In one embodiment, the wall positioned between the metal plate and theplasma is an upper wall of the chamber, e.g., a TCP window.

[0064] The present invention further provides methods for optimizingoperation of an inductively coupled plasma etching apparatus. In thesemethods, a chamber for etching a wafer is supplied. A window is attachedto a top opening of the chamber. The window has an outer surface and aninner surface that is exposed to an inner region of the chamber. A coilis placed over the window and a metal plate is placed over the outersurface of the window. The metal plate is positioned in a spaced apartrelationship between the coil and the outer surface of the window. Inaccordance with a first optimization method, the metal plate isconnected to a connection location on the coil. The connection locationis between an input terminal and an output terminal and is optimallyselected so as to produce substantially uniform incident ion energyproximate to the inner surface of the window. The substantially uniformincident ion energy is configured to reduce sputtering of the innersurface of the window while substantially simultaneously preventingdeposition of etch byproducts on the inner surface of the window. Inaccordance with a second optimization method, a controlled peak-to-peakvoltage is applied to the metal plate so as to produce substantiallyuniform incident ion energy proximate to the inner surface of thewindow. Again, the substantially uniform incident ion energy isconfigured to reduce sputtering of the inner surface of the window whilesubstantially simultaneously preventing deposition of etch byproducts onthe inner surface of the window.

[0065] The inductively coupled plasma etching apparatus of the presentinvention is well suited for plasma etching of recently developed devicematerials (e.g., platinum, ruthenium, and the like) that generatenonvolatile, electrically conductive reaction products (e.g., RuO₂). Itwill be apparent to those skilled in the art that the inductivelycoupled plasma etching apparatus of the present invention also may beused to plasma etch standard materials such as metal and polysilicon. Inthe plasma etching of metal and polysilicon, V_(pp) is adjusted torealize uniform and minimum deposition. In this manner, the mean waferbetween clean (MWBC) and the lifetime of the TCP window may be improved.

[0066] It will be apparent to those skilled in the art that the precisecontrol of V_(pp) and the resulting balance of sputtering and depositionon the TCP window provided by the apparatus and methods of the presentinvention provide numerous other advantages including the reduction ofproblems associated with particles and contamination, etch profilecontrol (by controlling the etch sidewall deposition coming from theplasma and the TCP window), etch selectivity control, and selective etchbyproduct deposition. In the case of selective etch byproductdeposition, this can be done by tuning V_(pp) so that materials havingcertain sticking coefficients and sputtering yields can be captured onthe TCP window to control etching, provided the surface of the TCPwindow is maintained at a relatively constant temperature.

[0067] In summary, the present invention provides an inductively coupledplasma etching apparatus and methods for optimizing the operation of aninductively coupled plasma etching apparatus. The invention has beendescribed herein in terms of several preferred embodiments. Otherembodiments of the invention will be apparent to those skilled in theart from consideration of the specification and practice of theinvention. For example, the location at which the Faraday shield plateis connected to the coil may be varied from the exemplary locationsshown and described herein to optimize a particular etch process. Theembodiments and preferred features described above should be consideredexemplary, with the scope of the invention being defined by the appendedclaims and their equivalents.

What is claimed is:
 1. A method for optimizing operation of aninductively coupled plasma etching apparatus, comprising: supplying achamber for etching a wafer; attaching a window to a top opening of thechamber, the window having an outer surface and an inner surface that isexposed to an inner region of the chamber; placing a coil over thewindow; placing a metal plate over the outer surface of the window, themetal plate being positioned in a spaced apart relationship between thecoil and the outer surface of the window; connecting the metal plate toa connection location on the coil, the connection location being betweenan input terminal and an output terminal and being optimally selected soas to produce substantially uniform incident ion energy proximate to theinner surface of the window, the substantially uniform incident ionenergy being configured to reduce sputtering of the inner surface of thewindow while substantially simultaneously preventing deposition of etchbyproducts on the inner surface of the window.
 2. A method foroptimizing operation of an inductively coupled plasma etching apparatus,comprising: supplying a chamber for etching a wafer; attaching a windowto a top opening of the chamber, the window having an outer surface andan inner surface that is exposed to an inner region of the chamber;placing a coil over the window; placing a metal plate over the outersurface of the window, the metal plate being positioned in a spacedapart relationship between the coil and the outer surface of the window;and applying a controlled peak-to-peak voltage to the metal plate so asto produce substantially uniform incident ion energy proximate to theinner surface of the window, the substantially uniform incident ionenergy being configured to reduce sputtering of the inner surface of thewindow while substantially simultaneously preventing deposition of etchbyproducts on the inner surface of the window.